A Dft Study on the Structural Properties and Co2 Electrocatalytic Reduction Activity of Monolayer Graphitic Carbon Nitride Supported Ag/Au Single Atom Catalysts

Abstract

In this study, the DFT has been utilized to research the structural characteristics and CO2 reduction performances of g-C3N4 supported Ag and Au single-atom electrocatalysts, namely Ag-C3N4 and Au-C3N4 respectively. The constructed structures have been optimized and both the electron density and charge density difference have been calculated, confirming the stability of the constructed single-atom catalysts (SACs). As demonstrated by charge density difference analysis, the CO2 undergoes chemical adsorption on Ag-C3N4 and Au-C3N4, resulting in the activation of CO2. Furthermore, the microscopic mechanisms for the formation of HCOOH, CO, CH3OH and CH4 from electrocatalytic CO2 reduction reaction (CO2RR) on these SACs have been fully investigated. Specifically, all structures of the reactants, products, and intermediates have been optimized, and their adsorption energy, zero-point energy, and free energy changes have been calculated. Subsequently, the product selectivity differences between Ag-C3N4 and Au-C3N4 catalysts are compared. Our findings show that Ag-C3N4 catalyzes CO2 to CH3OH and CH4 with similar efficiency, while Au-C3N4 more effectively facilitates the conversion of CO2 to CH3OH over HCOOH and CH4. Furthermore, by analyzing the free energy change values of rate-determining step for generating four types of C1 products, we find that Ag-C3N4 exhibits superior CO2 catalytic performance over Au-C3N4. Moreover, the hydrogen evolution reaction (HER) on these catalysts has been investigated, revealing that HER is inhibited on both catalyst surfaces. This finding emphasizes the preferential electrocatalytic reduction of CO2 on these catalysts. Through calculations of the energy band and density of state of the catalysts, it is found that the energy gap of Ag-C3N4 is smaller than that of Au-C3N4. This correlation suggests that a smaller energy gap is indicative of stronger catalytic activity, which is further evidenced by the higher activity of Ag-C3N4 in the electrocatalytic reduction of CO2 compared to Au-C3N4. Our results reveal that both Ag-C3N4 and Au-C3N4 exhibit strong activity in the electrocatalytic CRR. These results establish a theoretical basis for the development of single-atom catalysts (SACs) that can efficiently reduce CO2 through electrocatalysis.

Keywords: g-C3N4, Single atom catalysts, Density Functional Theory, CO2 reduction reaction, Electrocatalysis